This application claims the benefit of Korean Application No. P2000-86398, filed on Dec. 29, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a message transmission system and, more particularly, to an apparatus and method of preventing data traffic congestion in a message transmission system.
2. Background of the Related Art
In general, a bus access arbiter, of a master module, arbitrates bus access for transmitting a message from one functional module to another module, in a message transmission system of a private branch exchange system. Additionally, the message is transmitted through a Frame Synchronous (S) signal, which is generated by a master bus controller. The system is able to provide both a serial and a parallel message transmission method.
FIG. 1 illustrates a message transmission system of a background art, private branch exchange system. The system includes a master module 20 and N slave modules 30_1, 30_2, . . . , 30_N. The master module 20 and all of the slave modules are connected to the common bus (CB) 5 and the control line (CL) 10.
There are two ways for the module to connect to the CB 5, a serial line (SL) connection and a parallel line (PL) connection. The SL connection uses only one of the CB lines, and the PL connection uses all of the CB lines. The master module 20 is connected to all of the CB lines. Each of the N slave modules can be connected to the CB 5 using the SL or PL connection. The CL 10 includes a clock signal, a parity error signal, a busy signal, a frame synchronization signal, and many other signals.
Similar to the slave modules 30_1-30_N, the master module 20 can make a request for message transmission and is included in a node to communicate a message. Additionally, the master module 20 arbitrates access to the CB 5. The master module 20 shown in FIG. 1 includes a master bus controller 21, a CPU 22, and a shared memory 23, as shown in FIG. 2.
The master bus controller 21 includes a serial/parallel controller 21_1, a message transmitting/receiving controller 21_2, a memory arbiter 21_3, and a bus request arbiter 21_4. In addition, the bus request arbiter 21_4 includes an access authorizing block 21_4a and a request storage 21_4b, as shown in FIG. 3.
Reference will now be made in detail to the method of operating the message transmission system of the background art, private branch exchange system. We know that only one node may use the CB 5 for a given period of time. Therefore, a node must initially obtain a right to access the CB 5, to send a message to another node through the CB 5.
The bus request arbiter 21_4, of the master bus controller 21 shown in FIG. 2, receives an access-requesting signal from each module shown in FIG. 1. Based on this signal, the bus request arbiter 21_4 provides a selected module access to the CB 5.
The request storage 21_4b, of the bus request arbiter 21_4 shown in FIG. 3, stores the access requesting signals, sent by the access requesting modules, in the order that they are received in a given period of time. After all the requesting signals are stored in the request storage 21_4b, the access authorizing block 21_4a gives a bus access approval to a node, which is selected using a given selecting rule.
In addition, the master bus controller 21 provides frame synchronization and clock signals to the slave modules, which they use to send or receive information. Therefore, the slave modules are able to receive the data provided through the CB 5 and determine whether their access request is approved.
When the master bus controller 21 approves the access request of a node, the transmitting node transmits a node number of the receiving node. Thereafter, the receiving node sends information regarding its preferred receiving method to the master module 20, through the CB 5. Then, master module 20 informs the transmitting module of the preferred method. Finally, the transmitting module transmits the message to the receiving module, using the preferred message transfer method (i.e., a serial or parallel transfer method).
However, this method of transmitting a message in a message transmission system of the background art, private branch exchange has several disadvantages. If there is only one node sending an access-requesting signal, the master bus controller 21 gives an access right immediately after it receives the requesting signal. Then, the node may use all of the bandwidth of the bus. In this case, data traffic congestion may occur in the node. Even a single slave node, having such congestion, may cause the whole system to be unstable.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.